1. Field of the Invention
The present invention relates to controlling particle absorption on a wafer sample, and more particularly to controlling particle absorption on a wafer sample being inspected by a charged particle beam imaging system.
2. Description of the Prior Art
As electronic devices become smaller in size, the processing technique thereof becomes more microscopic. Charged particle beam imaging will likely become one of the critical technologies in advanced semiconductor manufacture. Charged particle beam imaging tools, which include conventional scanning electron microscopes (SEMs) have a much higher resolution than optical tools and are able to detect smaller size defects.
Particles such as dust in atmosphere influence the characteristics or yield of manufactured electronic devices significantly. Due to this, elimination of particles during the manufacturing process is a very important factor. In a microscopic circuit, since the sizes of particles are as large as or even larger than the distance between metal wires, yield (ratio of source material to product) is degraded when particles are adhered to the wafer causing short circuits or other problems.
Conventional methods for removing particles from, for example, a wafer chuck in a testing apparatus include the use of an air gun or nozzle to blow particles away from the chuck. However, this method is only partially effective in removing the particles from the chuck, especially those carrying charges.
Hence, how to control particle absorption on a wafer sample within a charged particle beam imaging system is now urgently needed to target.
Ezumi et al. (U.S.20040211899) disclosed a charged particle beam irradiation method for reducing the focus offset, magnification fluctuation and measurement length error in charged particle beam devices. In claim 11 of Ezumi, there disclosed a holder configured for gripping a sample and constructed to reach electrical ground during measurement of electrical potential. However, Ezumi did not disclose that the wafer sample was grounded.
To be specific, in [0005] of Ezumi, there disclosed that the cause of this static or electrostatic charge may for example be due to a fixed electrical potential from splitting (split polarization) of polarized material within the resist due to friction during applying of the resist coating by a spin coater.
In [0050] of Ezumi, there disclosed that the static electrometer probe measures the voltage of both the wafer and the grounded conveyor arm (also referring to FIGS. 2 and 4) so that a more accurate value can be obtained by calibrating the wafer electrical potential based on the ground potential of the conveyor arm and the static electrometer probe measures the voltage of both the wafer and the grounded conveyor arm so that a more accurate value can be obtained.
FIGS. 2 and 4 of Ezumi are directed for sample electrification measurement, therefore once both of the wafer and the conveyor arm are grounded to be electrically neutral, there would be no potential difference between the wafer and the conveyor arm such that no measurement result can be obtained. Since the wafer and the grounded conveyor arm can not be simultaneously grounded, i.e. both be electrically neutral, for voltage measurement and Ezumi has disclosed a grounded conveyor arm, the wafer sample is not possibly being grounded.
In addition, in FIG. 3 of Ezumi, it needs a distribution function for the electrical potential that was made based on this acquired data to determine a retarding voltage. Therefore, once the wafer sample is grounded, the distribution function and the subsequent procedure for determining the retarding voltage would no longer be needed.
Therefore, what Ezumi taught is directed to measuring the surface electrical potential with a grounded conveyor arm but Ezumi failed to disclose the wafer sample electrically neutral by grounding, and particularly, Ezumi failed to disclose keeping the wafer sample electrically neutral by grounding during transfer-in and transfer-out process. In other words, in the case of wafer samples being thoroughly grounded during transfer-in and transfer-out process, the sample electrification measurement method provided by Ezumi for correcting retarding voltage during measurement using charged particle beam in SEM is no longer needed.